1. Field of the Invention
The present invention relates to a sliding contact part for a recording medium, and more particularly to a sliding contact part such as a thermal head or a magnetic head adapted to contact with a recording medium in the form of a tape, disk or sheet and slide relative thereto.
2. Description of the Prior Art
Now commercially available are various devices for performing recording or reproduction with use of a recording medium such as a magnetic layer carrying sheet or film or a sheet of paper. Such recording/reproducing devices employ many parts adapted to always or temporarily slide on the recording medium relative thereto. This kind of parts includes a head slider for a flexible disk, a flying slider for a hard disk, a thermal head of a thermal printer, or a magnetic head. These parts are required not to damage the recording medium and to have a superior durability such that no wearing occurs even in long-term use.
Such a sliding contact part has a portion adapted to contact with the recording medium and slide :relative thereto. The sliding contact portion is covered with a wear resistance layer for suppressing wear of the sliding contact portion. The wear resistance layer is formed of a material such as Ta.sub.2 O.sub.5 or SiO.sub.2, but the wear resistance is insufficient.
Now, a conventional thermal head as an example of such a sliding contact part will be described in detail.
In general, a thermal head has the advantages of low noise, low cost, maintenance saving, power saving and high print quality. Then, in recent years, a thermal head has widely been applied to various recording equipments such as facsimiles and printers for word processors. On the other hand, these equipments have been increasingly demanded to have the performances of compact size, low cost, power saving, high print quality and long service life. Accordingly, the thermal head is also demanded to enhance its performances of compact size, low cost, high efficiency, high print speed, high print quality and long service life.
In particular, the performances of high print speed, high print quality and long service life are strongly demanded in the thermal head for the thermal printer. The high print speed and the high print quality are realized by designing the shape of the thermal head so as to project heating elements for effecting printing on the recording medium and by using means for increasing the contact pressure of the heating elements against the recording medium.
In the thermal head thus improved in print speed and print quality, however, the heating elements projected are remarkably worn by the increased contact pressure against the recording medium, causing the service life of the thermal head to become very short. To cope with this problem, it is essential to provide a protective layer superior in wear resistance on the thermal head.
Conventionally, such a protective layer used for a thermal head is formed of Ta.sub.2 O.sub.5, SiC, Si-O-N, SiAlON, etc. However, these materials are inferior in wear resistance against a thermal recording paper in particular. Thus, the conventional thermal head has a serious problem that the even balance between print quality and service life cannot be obtained. The inferiority in wear resistance of the protective layer in the conventional thermal head is considered to be due to the fact that the material (e.g., Ta.sub.2 O.sub.5) of the protective layer is apt to be broken by the friction to the material (e.g., CaCO.sub.3 or SiO.sub.2) contained in the thermal recording paper.
In order to extend the service life of the thermal head at the sacrifice of the print quality, it has been tried to reduce an amount of projection of the heating elements to thereby increase a contact area of portions other than the heating element adapted to contact with the recording medium, or reduce the contact pressure against the recording medium, or increase the film thickness of the protective layer, thus suppressing the wear of the protective layer. However, as especially in a thermal transfer printer using an ink ribbon for a word processor, it is demanded to realize high print quality on a post card, a so-called rough paper having a low surface smoothness, etc., but the high print quality cannot be expected because of the occurrence of blur or the like. Thus, the compatibility between high print quality and long service life cannot be attainable even by employing the above-mentioned means for extending the service life.
As mentioned above, the wear of the protective layer against a thermal recording paper is large in the conventional thermal head, and so the print quality in using an ink ribbon is necessarily reduced. Further, the demand for high-speed printing in the thermal printer has recently been increased to limit the shape of the thermal head and develop a reduction in print efficiency. Thus, the even balance between print quality and service life becomes further difficult to obtained.
While the above description has been directed to the conventional thermal head, other sliding contact parts in the prior art have similar defects such that the wear resistance is insufficient to shorten the service life.